As a nuclear power plant in the past, a nuclear power plant including a pressurized water reactor is known. In this nuclear power plant, a primary cooling system such as the pressurized water reactor or a steam generator is stored in a reactor container (see, for example, Non-Patent Document 1). A spray facility for spraying spray water into the reactor container is provided around the nuclear container on the assumption of an abnormal situation.
As shown in FIG. 10, this spray facility includes a water tank for refueling disposed on the outside of the reactor container and serving as a water source, a spray ring disposed in the reactor container, a first spray pipe that connects the water tank for refueling and the spray ring, and a spray pump interposed in the first spray pipe. A storage container recirculation sump that is provided at the bottom of the reactor container and stores the sprayed spray water is provided in this spray facility. The storage container recirculation sump is connected to the first spray pipe between water tank for refueling and the spray pump via a second spray pump.
If an abnormal situation occurs, the pressure in the reactor container is increased by an evaporated primary coolant (light water). In such a case, the spray facility operates, more specifically, the spray pump is driven to spray the spray water from the water tank for refueling into the reactor container via the spray ring, whereby the inside of the reactor container is cooled to reduce the pressure in the reactor container. Thereafter, the sprayed spray water is stored in the storage container recirculation sump and the stored spray water is sprayed from the spray ring again through the second spray pipe. In other words, the spray facility is configured such that the spray water circulates in the reactor container.
In the spray facility, to remove radioactive iodine contained in the evaporated light water, an iodine removal chemical tank that stores an iodine removal chemical, a spray eductor interposed in the first spray pipe, a chemical injection flow path that connects the iodine removal chemical tank and the spray eductor, and an on-off valve interposed in the chemical injection flow path are provided. Consequently, at abnormal time, the on-off valve is opened and the iodine removal chemical is injected into the first spray pipe via the spray eductor to mix the iodine removal chemical and the spray water. The mixture of the iodine removal chemical and the spray water is sprayed into the reactor container to remove the radioactive iodine in the reactor container.
In this case, in general, strong alkali caustic soda is used as the iodine removal chemical. Therefore, to reduce burdens of management and operation of the chemical and a test of a chemical injection line valve, a pH adjusting system described below is also adopted.
For example, it is known that a mesh basket containing a pH adjuster such as trisodium phosphate is arranged on a base level near an outer peripheral wall in the nuclear reactor (on a floor of the storage container recirculation sump) (see, for example Non-Patent Document 2). With this configuration, when the spray water is sprayed by the spray facility at abnormal time, the storage container recirculation sump is filled with the spray water. Then, the basket disposed on the floor of the storage container recirculation sump is submerged and the pH adjuster stored in the basket dissolves in the spray water. Thereafter, the spray water in which the pH adjuster dissolves is circulated in the reactor container by the spray facility. This makes it possible to adjust pH in the reactor container. The radioactive iodine can be kept in the solution by adjusting pH in the reactor container.
The deterioration in durability of structural materials and various devices in the reactor container can be controlled by adjusting pH in the reactor container. Boric acid is dissolved in the light water to decelerate neutrons generated by the nuclear fission reaction. Therefore, the light water is low in pH and acidic. The recirculated water is likely to deteriorate durability of materials of devices and pipes that recirculate the light water for a long period after an accident. However, the deterioration in durability of the devices and the pipes can be controlled by adjusting pH in the reactor container to be neutral.    Non-Patent Document 1: “Genkai Nuclear Power Plant, Application for Permission of a Change in the Nuclear Reactor (A Change in Nos. 3 and 4 Nuclear Reactor Facilities)”, Kyushu Electric Power Co., Inc., April 1990, Attached Document 8, p. 8-5-8 to 8-5-10 and p. 8-5-18 Non-Patent Document 2: J. A. Reinhart Site Director/Fort Calhoun Station, “Fort Calhoun Station, Unit No. 1 License Amendment Request (LAR) ‘Change of Containment Building Sump Buffering Agent from Trisodium Phosphate to Sodium Tetraborate’”, [online], Aug. 21, 2006, U.S.NRC, [retrieved on Oct. 17, 2007], Internet <URL: http://www.nrc.gov/→select Electrpnic Reading Room→select Documents in ADAMS→select Web-based access→select Begin ADAMS Search→Input “ML062340039”→select Rank 5. (80)>